Block header binary encoding
The binary format for chain graphs of degree three is defined in Chainweb.BlockHeader.
| Size | Bytes | Value |
|---|---|---|
| 8 | 0-7 | flags |
| 8 | 8-15 | time |
| 32 | 16-47 | parent |
| 110 | 48-157 | adjacents |
| 32 | 158-189 | target |
| 32 | 190-221 | payload |
| 4 | 222-225 | chain |
| 32 | 226-257 | weight |
| 8 | 258-265 | height |
| 4 | 266-269 | version |
| 8 | 270-277 | epoch start |
| 8 | 278-285 | nonce |
| 32 | 286-317 | hash |
total: 318 bytes
Adjacent parents record
The binary format for adjacent parents (length 3):
| Bytes | Value |
|---|---|
| 0-1 | length |
| 2-109 | adjacents |
total: 110 bytes
Adjacent parent
| Bytes | Value |
|---|---|
| 0-3 | chain |
| 4-35 | hash |
total: 36 bytes
Proof of work and field values
Arithmetic operations and comparisons on parent, target, weight, and hash interpret the value as unsigned 256-bit integral numbers in little endian encoding.
All operations are performed using rational arithmetic of unlimited precision and the final result is rounded.
For details about how the result is rounded, consult the source code directly.
Time stamps
The time and epoch start values are a little endian twos complement encoded integral numbers that count SI microseconds since the start of the POSIX/UNIX epoch (leap seconds are ignored).
These numbers are always positive (highest bit is 0).
Numbers
The height is a little endian encoded unsigned integral 64 bit number.
The length is a little endian encoded unsigned integral 16 bit number.
Version
The version field identifies the Chainweb version.
It is a 32 bit value in little endian encoding.
Values up to 0x0000FFFF are reserved for production versions, including includes development and testnets.
| Value | Version |
|---|---|
| 0x00000005 | mainnet01 |
| 0x00000001 | development |
| 0x00000007 | testnet04 |
Other
The nonce is any sequence of 8 bytes that is only compared for equality.
The chain is any sequence of 4 bytes that identifies a chain and can be compared for equality.
The payload is any sequence of 32 bytes that is a cryptographic hash of the payload associated with the block and can be compared for equality.
flags are eight bytes of value 0x0 that are reserved for future use.
Work header binary encoding
The work bytes received from the /miner/work endpoint is slightly different than the above header format.
These headers do not include the block hash, instead prefixing the header above (without hash) with chain id and hash target bytes.
The first 36 bytes are informational. Only the bytes from position 36 to the end are the subject of the proof of work hash computation.
The final 8 bytes are the nonce. The creation time is encoded in bytes 44-52 (see above for details of the encoding). Miners are allowed, but not required, to update the time to reflect the solve time for the block more closely. A larger value for the creation time increases the accuracy of the difficulty adjustment which is in the interest of miners. The high difficulty guarantees that the outcome of the race of winning blocks is determined by actual hash power. However, blocks that are predated (that is, have a creation time that is in the future) are rejected during block header validation. Leaving the time unchanged is a valid choice.
Miners must not change or make any assumptions about the content of the "reserved" bytes.
Defined in Chainweb.Miner.Core:
| Size | Bytes | Work bytes | Value |
|---|---|---|---|
| 4 | 0-3 | NA | chain |
| 32 | 4-35 | NA | hash-target |
| 8 | 36-43 | 0-7 | reserved |
| 8 | 44-51 | 8-15 | time |
| 298 | 52-313 | 16-277 | reserved |
| 8 | 314-321 | 278-285 | nonce |
total: 322 bytes
For arithmetic comparisons the hash-target is interpreted as unsigned 256 bit integral number in little endian encoding.
The time is a little endian twos complement encoded integral number that counts SI microseconds since the start of the POSIX/UNIX epoch (leap seconds are ignored). The value is always positive (highest bit is 0).